As semiconductors for use in transistors or the like, semiconductor thin films containing oxide such as indium oxide, gallium oxide and tin oxide have been traditionally known. Such a semiconductor thin film can be formed at low temperature as compared to a semiconductor such as silicon. Thus, a device having a substrate made of a heat-labile resin material can be designed (for instance, see Patent Documents 1 to 7).
Patent Documents 1 to 7 disclose that: an oxide film for use as a semiconductor thin film is formed of amorphous oxide that contains, for instance, indium, zinc and gallium; the amorphous oxide also contains fine crystals and has an electron carrier concentration of less than a predetermined value; and the oxide film is formed in an oxygen atmosphere having a predetermined concentration.
In addition, Patent Document 5 discloses an oxide film obtained by forming an amorphous oxide thin film and then irradiating the amorphous oxide thin film with an oxygen-containing plasma.    Patent Document 1: JP-A-2006-165527    Patent Document 2: JP-A-2006-165528    Patent Document 3: JP-A-2006-165529    Patent Document 4: JP-A-2006-165530    Patent Document 5: JP-A-2006-165531    Patent Document 6: JP-A-2006-165532    Patent Document 7: JP-A-2006-173580